Water-Based Lubrication For Hot Forming

ABSTRACT

A manufacturing control system is arranged to cause an aluminum alloy blank to be heated to at least its solvus temperature, to cause a die set to be sprayed with a lubricant formulation that includes water, lubricant, and a surfactant, to cause the blank to be positioned in the die set while heated such that the blank does not touch the die set, and to cause the die set to close on the blank to form the blank into a part while quenching the part.

TECHNICAL FIELD

This disclosure relates to hot forming of aluminum alloy parts and lubricant formulations used therefor.

BACKGROUND

Automotive body panels have long been made from mild steels. Aluminum alloy body panels, however, have been increasing in popularity given their light weight. 5xxx and 6xxx series aluminum alloys, which are aluminum-magnesium and aluminum-magnesium-silicon alloys, have been of interest in this regard as they may be shaped and processed by methods consistent with those of mild steel.

Aluminum-zinc alloys of the 7xxx series at T6 or T7x tempers have strengths similar to those of high and ultra-high strength steels and can achieve yield strengths exceeding 400 MPa. T6 and T7x temper aluminum-zinc alloys, however, cannot be conventionally stamped as these alloys have little to no formability at room temperature.

SUMMARY

In one embodiment, a method includes heating an aluminum alloy blank to at least its solvus temperature, spraying portions of a die set with a lubricant formulation that includes water, lubricant and a surfactant, positioning the blank in the die set while heated such that the blank does not touch the die set, and closing the die set on the blank to form the blank into a part while quenching the part.

In another embodiment, a manufacturing system includes a furnace or oven configured to heat an aluminum alloy blank to at least its solvus temperature, a die set, and a nozzle arrangement configured to spray portions of the die set with a lubricant formulation that includes water, lubricant and a surfactant. The system also includes a transfer mechanism configured to position the blank in the die set while heated such that the blank does not touch the die set, and an actuator configured to close the die set on the blank to form the blank into a part while quenching the part.

In yet another embodiment, a manufacturing control system includes one or more controllers. The one or more controllers are configured to heat an aluminum alloy blank via a heater to at least its solvus temperature, to spray portions of a die set via a nozzle with a lubricant formulation that includes water, lubricant, and a surfactant, to position the blank in the die set while heated via a transfer mechanism such that the blank does not touch the die set, and to close the die set on the blank via an actuator to form the blank into a part while quenching the part

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a hot forming station.

FIG. 2 is a block diagram of the hot forming station of FIG. 1.

FIG. 3 is a flow chart of an algorithm for hot forming an aluminum alloy blank.

DETAILED DESCRIPTION

Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the embodiments.

As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures can be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations.

So called “hot forming” has been used to shape, for example, F-temper 6xxx or 7xxx series aluminum alloy blanks into automotive components. In one example, an F-temper 7xxx series aluminum blank is heated to at least its solvus temperature and then positioned in a die set so as to not touch the die set. The die set is then closed to form the blank while also quenching it.

Lubricants are often used in sheet forming applications. They can reduce friction between blank and die, which allows for smooth and controlled metal flow. And, they can assist with part removal, remove undesired heat, and extend die life. Lubricant choice and application within the context of hot forming aluminum alloy operations, however, can be more complicated as compared with warm forming aluminum alloy operations due to the high blank temperatures achieved prior to hot forming. (These temperatures can exceed 250° C.—a temperature at which certain lubricants may no longer function.) Here, lubricants of particular formulation are applied to dies of hot forming stations as explained in more detail below.

With reference to FIG. 1, a manufacturing system 10 for forming a blank 12 includes a heating apparatus 14, a transfer mechanism 16, and a die set 18. In one example, the blank 12 is an F-temper 7xxx series aluminum alloy blank. Other alloys, however, are also contemplated. The heating apparatus 14, as the name suggests, heats the blank 12, and may be an industrial furnace or oven capable of producing internal temperatures high enough to the heat blanks 12 placed therein to a predetermined temperature, such as a solution temperature of the blanks 12. In certain circumstances, however, the heating apparatus 14 may not heat the blanks 12 past their liquidus (melting) temperature.

The solution temperature for a 7xxx series aluminum alloy may be approximately 450° C. to 490° C. The solution temperature (or solid solution temperature) is the temperature at which a substance is readily miscible, which is the property of materials to mix in all proportions forming a homogeneous solution.

The solidus temperature is the collection of temperatures on a phase diagram below which a given substance is completely solid. The solidus temperature quantifies the temperature at which melting of a substance may begin, but not the temperature at which the substance is melted completely. With some materials, there may be a phase existence between the solidus and liquidus temperatures such that the substance consists of solid and liquid phases simultaneously. The closer the material temperature is to the solidus temperature, the more the material is in a solid phase. The closer the material temperature is to the liquidus temperature, the more the material is in a liquid phase. As such, the blank 12 may be heated to at least its solvus temperature but less than its solidus temperature to provide a blank that is substantially solid to facilitate handling and transport yet more readily formable The solvus temperature indicates the limits of solubility of hardening alloy elements into the aluminum matrix. Above the solvus temperature, for a given alloy, is the solid solution temperature range.

The transfer mechanism 16 may be configured to move and position the blank 12. The transfer mechanism 16, in some examples, may be a manipulator such as a robot, an arm, or conveyor arrangement. The transfer mechanism 16 may be configured to quickly transfer the blank 12 from the heating apparatus 14 to the die set 18 to reduce the opportunity for heat loss from the blank 12. For example, the system 10 and transfer mechanism 16 may be configured such that the temperature of the blank 12 does not decrease to or below its critical quench temperature—the temperature at which quenching must begin to achieve a proper quench of the material. The critical quench temperature for most 7xxx series aluminum alloys, for example, is approximately 400° C.

The die set 18 is provided to form the blank 12 into a part having a predetermined shape. The die set 18, in some examples, includes a first die 20, a second die 22, at least one actuator 24, and a staging apparatus 26. The first and/or second dies 20, 22 are configured to form the blank 12 into the predetermined shape. The actuator 24 actuates the first die 20 and/or the second die 22 toward or away from each other and provides force to form the blank 12. The actuator 24 may be of any suitable type, such as hydraulic, pneumatic, mechanical, electromechanical, or combinations thereof. The die set 18 and actuator 24 collectively may also be referred to as a machine press, stamping press, or quenching press.

The staging apparatus 26 may be provided for positioning the blank 12 between and spaced apart from the first and second dies 20, 22. As such, the staging apparatus 26 may inhibit conductive heat transfer between the blank 12 and the die set 18, thereby helping to maintain the blank 12 at or above its critical quench temperature. The staging apparatus 26 may receive the blank 12 from the transfer mechanism 16 and may release the blank 12 as the first die 20 and/or the second die 22 are closed and engage the blank 12. In addition, the system 10 may be configured such that little heat is lost from the blank 12 between removal from the heating apparatus 14 and closing of the die set 18. In one example, the temperature of the blank 12 may decrease by less than 10° C. The blank 12, however, could experience a greater temperature loss, such as up to a 90° C. assuming that the blank 12 is heated to 490° C. and the critical quench temperature is 400° C.

The die set 18 may include piping 28 that facilitates cooling of the first and/or second dies 20, 22 and quenching of the part formed from the blank 12. The piping 28 may be voids or channels formed into the die set 18, or any combination of externally connected piping and channels. The piping 28 may be connected to a cooling source and may receive a heat transfer medium, such as a fluid, from the cooling source for cooling the die set 18 to a desired temperature (e.g., 1° C. to 30° C.). The die set 18 may be cooled in a manner that inhibits formation of condensation on one or more surfaces thereon. In a mass production setting, the temperature of the die set 18 may be cooled to the predetermined temperature range before forming and quenching a blank to remove heat that may have been transferred from a previous blank to the die set 18.

Forming the heated blank 12 into a part may occur simultaneously with quenching of the part. The quench rate affects the final temper strength and corrosion performance of the material. In some embodiments, the quench rate for an aluminum alloy, as it transitions for example from 400° C. to 290° C., may be equal to or greater than 150° C. per second. The part may be further cooled to a final temperature from 200° C. to 25° C. before removal of the part from the die set 18 to provide dimensional stability during subsequent processing.

The system 10 may be designed to operate continuously with a number of blanks being heated in series or parallel by one or more heating apparatuses and then transferred to at least one die set for forming and quenching. At least one of the die sets may become hotter than 30° C. during, or after, blank forming.

The part may be removed from the die set 18 by the transfer mechanism 16, another transferring device, or by hand. The part then proceeds on to subsequent processing which may include flanging, trimming, and natural and/or artificial aging to bring the aluminum alloy part to a high strength temper such as T6 or T7x.

To improve the quench and metal flow behavior during forming, a water-based lubricant is applied (e.g., sprayed) onto the dies 20, 22 prior to closing of the die set 18 around the blank 12 (e.g., prior to the transfer mechanism positioning the blank between the dies 20, 22). Because most production die sets, such as the die set 18, can have miscellaneous oils and grease thereon from maintenance activities and anti-corrosion treatments, a surfactant is added to the lubricant formulation to maintain the local as-applied coating weight prior to hot stamping.

Because the lubricant formulation is water based, it does not build up on the surface of the dies 20, 22 to the same extent as non-water based formulations: the die faces remain relatively clean and do not require frequent cleaning. Other benefits include that (i) the dies 20, 22 may be cleaned with hot (e.g., 60° C.) water without a degreaser, (ii) the water may contain an alkaline or acid concentrate to support proper surface preparation for subsequent pretreatment or paint processes, (iii) no solvent-based VOC or smoke will be produced during the quenching process, (iv) the coating weight and lubricant concentration may be varied on different areas of the dies 20, 22 via spot application to support formability and quench efficiency, and (v) the process window and robustness may be increased via more uniform quench rates and larger die face overcuts.

In one example, the lubricant is a die lubricant normally used in forging applications (e.g., FORGE EASE AL 278). It was initially discovered that this lubricant performed well when diluted with isopropyl alcohol (IPA) with a concentration of 1:3 (lubricant:IPA) and applied to aluminum alloy blanks prior to warm forming. As such, this formulation was attempted within the context of hot forming. The lubricant formulation, however, was applied to the die set as opposed to the blanks because of the high blank temperatures associated with hot forming. Although favorable results were achieved, it was noted that IPA can be flammable. An alternative to IPA was thus sought.

A surfactant that is a combination of an acetylenic diol and an alcohol ethoxylate (e.g., DYNOL 800) was found to be a suitable replacement for IPA. That is, non-ionic surfactants are expected to be preferable to anionic or cationic surfactants. In one example, a ratio of water to lubricant to surfactant of 90% water, 10% lubricant and adding 3% surfactant was found to be effective. For example if the water/lubricant mixture is to be 3000 mL, then the amount of water would be 2700 mL, the amount of lubricant would be 300 mL, and the amount of surfactant would be 93 mL.

This lubricant formulation was able to be uniformly applied with no streaks or heavy film residue. Because the formulation is primarily water, the quench efficiency associated with the hot forming process is improved.

With reference to FIG. 2, the system 10 is shown to include one or more controllers 30 in communication with and operatively arranged to control the heating apparatus 14, transfer mechanism 16, actuator 24, and a spray nozzle arrangement 32. The controllers 30 may be a distributed set of processors or a single processor, etc. With further reference to FIG. 3, the controllers 30 at operation 34 may command the heating apparatus 14 to heat an aluminum alloy blank to at least its solvus temperature. At operation 36, the controllers 30 may command the spray nozzle arrangement 32 to spray the dies 20, 22 with a lubricant formulation such as those contemplated herein. As mentioned above, the concentration of lubricant can be varied to achieve different formability and quench efficiency objectives. For example, a lubricant formulation having relatively more lubricant can be initially applied by the spray nozzle arrangement 32 to certain portions of the dies 20, 22 while another lubricant formulation having relatively less lubricant can be subsequently applied by the spray nozzle arrangement 32 (or another spray nozzle arrangement) to other portions of the dies 20, 22. At operation 38, the controllers 30 may command the transfer mechanism 16 to position the blank while heated within the dies 20, 22 so that the blank does not come into contact with the dies 20, 22. And, the controllers 30 at operation 40 may command the actuator 24 to close the dies 20, 22 to form a part while quenching the part.

The processes, methods, logic, or strategies disclosed may be deliverable to and/or implemented by a processing device, controller, or computer, which may include any existing programmable electronic control unit or dedicated electronic control unit. Similarly, the processes, methods, logic, or strategies may be stored as data and instructions executable by a controller or computer in many forms including, but not limited to, information permanently stored on various types of articles of manufacture that may include persistent non-writable storage media such as ROM devices, as well as information alterably stored on writeable storage media such as floppy disks, magnetic tapes, CDs, RAM devices, and other magnetic and optical media. The processes, methods, logic, or strategies may also be implemented in a software executable object. Alternatively, they may be embodied in whole or in part using suitable hardware components, such as Application Specific Integrated Circuits (ASICs), Field-Programmable Gate Arrays (FPGAs), state machines, controllers or other hardware components or devices, or a combination of hardware, software and firmware components.

The words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments may be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics may be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes may include, but are not limited to cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications. 

What is claimed is:
 1. A method comprising: heating an aluminum alloy blank to at least its solvus temperature; spraying portions of a die set with a lubricant formulation that includes water, lubricant and a surfactant; positioning the blank in the die set while heated such that the blank does not touch the die set; and closing the die set on the blank to form the blank into a part while quenching the part.
 2. The method of claim 1, wherein the surfactant includes acetylenic diol.
 3. The method of claim 1, wherein the surfactant includes alcohol ethoxylate.
 4. The method of claim 1, wherein the lubricant formulation by volume includes more water than lubricant and surfactant.
 5. The method of claim 1, wherein the lubricant formulation by volume includes less than 5% surfactant.
 6. The method of claim 1, wherein the aluminum alloy blank is an F-temper aluminum alloy blank.
 7. The method of claim 6, wherein the aluminum alloy blank is an F-temper 6xxx aluminum alloy blank.
 8. The method of claim 6, wherein the aluminum alloy blank is an F-temper 7xxx aluminum alloy blank.
 9. The method of claim 1 further comprising cooling the die set to a temperature between 1° C. to 30° C.
 10. The method of claim 1, wherein the solvus temperature is at least 450° C.
 11. The method of claim 1, wherein the spraying includes spraying the portions with a first lubricant formulation and spraying other portions of the die set with a second lubricant formulation different than the first to obtain different formability and quench efficiency performance between the portions and other portions during the closing.
 12. A manufacturing system comprising: a furnace or oven configured to heat an aluminum alloy blank to at least its solvus temperature; a die set; a nozzle arrangement configured to spray portions of the die set with a lubricant formulation that includes water, lubricant and a surfactant; a transfer mechanism configured to position the blank in the die set while heated such that the blank does not touch the die set; and an actuator configured to close the die set on the blank to form the blank into a part while quenching the part.
 13. The system of claim 12, wherein the surfactant includes acetylenic diol.
 14. The system of claim 12, wherein the surfactant includes alcohol ethoxylate.
 15. The system of claim 12, wherein the lubricant formulation by volume includes more water than lubricant and surfactant.
 16. The system of claim 12, wherein the lubricant formulation by volume includes less than 5% surfactant.
 17. The system of claim 12, wherein the aluminum alloy blank is an F-temper aluminum alloy blank.
 18. The system of claim 17, wherein the aluminum alloy blank is an F-temper 6xxx aluminum alloy blank.
 19. The system of claim 17, wherein the aluminum alloy blank is an F-temper 7xxx aluminum alloy blank.
 20. The system of claim 12 further comprising piping configured to cool the die set to a temperature between 1° C. to 30° C.
 21. The system of claim 12, wherein the solvus temperature is at least 450° C.
 22. The system of claim 12, wherein the nozzle arrangement is further configured to spray other portions of the die set with another lubricant formulation to obtain different formability and quench efficiency performance between the portions and other portions to obtain different formability and quench efficiency performance between the portions and other portions.
 23. A manufacturing control system comprising: one or more controllers configured to heat an aluminum alloy blank via a heater to at least its solvus temperature, to spray portions of a die set via a nozzle with a lubricant formulation that includes water, lubricant, and a surfactant, to position the blank in the die set while heated via a transfer mechanism such that the blank does not touch the die set, and to close the die set on the blank via an actuator to form the blank into a part while quenching the part.
 24. The system of claim 23, wherein the surfactant includes acetylenic diol.
 25. The system of claim 23, wherein the surfactant includes alcohol ethoxylate.
 26. The system of claim 23, wherein the lubricant formulation by volume includes more water than lubricant and surfactant.
 27. The system of claim 23, wherein the lubricant formulation by volume includes less than 5% surfactant.
 28. The system of claim 23, wherein the aluminum alloy blank is an F-temper aluminum alloy blank.
 29. The system of claim 28, wherein the aluminum alloy blank is an F-temper 6xxx aluminum alloy blank.
 30. The system of claim 28, wherein the aluminum alloy blank is an F-temper 7xxx aluminum alloy blank.
 31. The system of claim 23, wherein the one or more controllers are further configured to cool the die set via piping to a temperature between 1° C. to 30° C.
 32. The system of claim 23, wherein the solvus temperature is at least 450° C.
 33. The system of claim 23, wherein the one or more controllers are further configured to spray other portions of the die set via a nozzle with another lubricant formulation to obtain different formability and quench efficiency performance between the portions and other portions. 